Circuit for detecting leakage in power supply

ABSTRACT

A power source device comprises a cell unit  12  comprising a plurality of cells  12   a . Connected between a positive side terminal and a negative side terminal of the cell unit  12  is a first current line  34  having two voltage dividing resistors  30, 32  interposed therebetween, and is a second current line  22  having two protection resistors  14, 16  and two detection resistors  18, 20  interposed therebetween. An intermediate point  24  of the second line  22  is grounded to a grounding  26  via an insulation resistor  28 . The voltage difference between a voltage (V 1 , V 2 ) detected by the detection resistors  18, 20  and a reference voltage (Vc) obtained from a point of connection  35  between the voltage dividing resistors is input to two Op-Amps  36, 38  serving as the input voltage (V 1 IN, V 2 IN). Based on the output voltage (V 1 OUT, V 2 OUT) obtained from the Op-Amps  36, 38 , leakage occurrence is detected.

TECHNICAL FIELD

The present invention relates to a leakage detection circuit for use ina power source device provided with an electric motor vehicle, and moreparticularly to a leakage detection circuit for use in a power sourcedevice comprising a plurality of cells.

BACKGROUND ART

Electric motor vehicles are recently provided with a cell unit servingas a power source for a drive motor and generating a high voltage of atleast 240 V. The cell unit has mounted an insulation member between theunit and a vehicle body, and is fixed to the vehicle body in a state offloating as electrically separated in order to avoid electrical shock tohumans. The cell unit becomes high in voltage as described above,encountering the problem of electric leakage i.e., short-circuitaccident between the cell and the vehicle body.

For example, electrolyte of the cell leaks out or, dust clinging to asurface of the cell, etc. is doused with water ingressing into thesurface while the vehicle is driven in rainy weather, to impairinsulation properties of the insulation member, causing such insulationfault that weak leak current flows, thereby impressing a high voltage ofthe cell unit on the vehicle body. This increases hazard including anelectric shock accident caused by human contact to the vehicle body, andspark occurrence caused by large current discharging with the contact ofan electrical conductive tool, etc.

It is conventional practice to detect electric leakage by providing aleakage detection circuit shown in FIG. 6. With the leakage detectioncircuit, a pair of resistors 5, 6 are connected to opposite ends of acell unit 1, respectively. An intermediate point between the resistors5, 6 is grounded to the grounding (vehicle body) via a resistor 2 fordetecting electric leakage.

The cell unit 1 comprises a plurality of secondary cells such as nickelhydrogen cells which are connected to one another in series, which islikely to cause breakdown between a point of interconnecting secondarycells and the ground. The breakdown occurrence at such a positionentails a problem of creating a dead zone wherein the leakage cannot bedetected, or of reducing detection sensitivity as will be describedbelow.

As shown in FIG. 6, a resistor 4 corresponds to breakdown occurrence atan intermediate point of the cell unit 1. Current flows through aleakage detection resistor 2 by way of 2 routes as indicated by an arrowin a solid line and by an arrow in a broken line. Suppose when thecurrents are i1, i2 as illustrated, the currents are expressed asfollows:

i 1=(B/2)/(Rs+R 1+R)

i 2=(B/2)/(Rs+R 2+R)

In the case where a value of resistance R1 for the resistor 5 is equalto a value of resistance R2 for the resistor 6, the two currents, i1 andi2 are equal in amount and are opposite in flowing direction, so that avoltage V1 detected is zero in spite of electric leakage occurrence.Even if a value of resistance for the resistor 5 is different from avalue for the resistor 6, the dead zone will be created when leakageoccurs at any point of connection between a plurality of cellsconstituting the cell unit 1.

In this case, the currents i1 and i2 flow in opposite directions eachother, as described above, so that a voltage V1 detected becomes asmaller value, making sensitivity reduced, making it difficult to detectthe voltage. Furthermore, when a voltage (+B) of the cell unit 1 varies,the voltage changes a detection value of leakage, whereby entailing aproblem that the leakage cannot be detected with high accuracy.

An object of the present invention is to provide a leakage detectioncircuit for use in a power source device comprising a cell unit of highvoltage, which circuit is adapted to detect reliably with a simplestructure leakage occurrence in a cell unit, and which is adapted topresume a portion of leakage.

DISCLOSURE OF THE INVENTION

A leakage detection circuit for use in a power source device embodyingthe present invention comprises:

a first current path being connected to opposite electrodes of the cellunit comprising a plurality of cells, and having a reference pointgenerating a reference voltage corresponding to potential differencebetween the opposite electrodes,

a second current path being connected to the opposite electrodes of thecell unit, and having three points which are different in potentialdifference, the three points of which an intermediate point is connectedto a grounding via an insulation resistor,

a first and second comparators having one input end to which voltage isapplied from each of the two points divided by the intermediate point ofthe second current path, and having the other input end to whichreference voltage is applied from the reference point of the firstcurrent path, and

a detection circuit detecting leakage occurrence based on outputs of thefirst and the second comparators.

With the leakage detection circuit of the invention described, supposethe leakage occurs at any point of connection between the plurality ofcells constituting the cell unit. There is no change in current flowingthrough the first current path, and the reference voltage generated atthe reference point is constant. On the other hand, in the secondcurrent path, leaking current flows from the intermediate point throughthe insulation resistor to the grounding (vehicle body), generatingchange in potential of the two points divided by the intermediate point,whereby outputs of the first and the second comparators are changed. Asa result, the leakage occurrence is detected.

Accordingly, even if leakage voltage varies along with magnitude ofleakage current, the leakage can be detected reliably since thereference voltage is fixed.

Stated specifically, a circuit constant of the first and the secondcurrent paths is so adjusted that in the event of leakage occurrence atany point of connection between the cells constituting the cell unit, adead zone in detecting leakage based on the outputs given by the firstand the second comparators is contained in an inside of potentialdistribution region corresponding to one cell, which is included inpotential distribution generated between opposite electrodes of the cellunit.

This eliminates the problem of the dead zone in the leakage detection.

A leakage detection circuit for use in a power source unit of theinvention comprises:

a first current line having opposite ends connected to oppositeelectrodes, respectively, of the cell unit, and having connected inseries each other first and second voltage dividing resistors, andhaving the resistors interposed between the opposite ends,

a second current line having opposite ends connected to oppositeelectrodes, respectively, of the cell unit, and having connected inseries sequentially a first protection resistor, a first detectionresistor, a second detection resistor, and a second protection resistor,and having the resistors interposed between the opposite ends,

a grounding connection line connecting to a grounding via an insulationresistor a point of connection between the first detection resistor andthe second detection resistor which are interposed on the second currentline,

a first comparator having one input end connected to a point ofconnection between the first protection resistor and the first detectionresistor which are interposed on the second current line, and having theother input end connected to a point of connection between the firstvoltage dividing resistor and the second voltage dividing resistor whichare interposed on the first current line,

a second comparator having one input end connected to a point ofconnection between the second detection resistor and the secondprotection resistor which are interposed on the second current line, andhaving the other input end connected to a point of connection betweenthe first voltage dividing resistor and the second voltage dividingresistor which are interposed on the first current line, and

a detection circuit detecting leakage occurrence based on outputs of thefirst and the second comparators.

With the leakage detection circuit of the invention described, supposethe leakage occurs at any point of connection between the plurality ofcells constituting the cell unit. There is no change in current flowingthrough the first current line, and a reference voltage generated at apoint of connection (reference point) between the first and the secondvoltage dividing resistors is therefore constant. On the other hand, inthe second current line, leaking current flows from a point ofconnection (intermediate point) between the first and the seconddetection resistors through the grounding connection line and theinsulation resistor to the grounding (vehicle body), generating changecorresponding to the magnitude of the leakage current in potentials of apoint of connection between the first protection resistor and the firstdetection resistor and in potentials of a point of connection betweenthe second detection resistor and the second protection resistor,whereby outputs of the first and the second comparators are changed. Asa result, the leakage occurrence is detected.

Accordingly, even if a leakage voltage varies along with the magnitudeof the leakage current, the leakage occurrence can be detected reliablysince the reference voltage is fixed.

Stated specifically, the first and the second comparators each outputstwo signals different in potential corresponding to magnitude relationbetween a voltage impressed to one input end and a reference voltageimpressed to the other input end. For example, the first comparatoroutputs a signal “high” when the voltage to be impressed to the oneinput end is greater than the voltage to be impressed to the other inputend. The second comparator outputs a signal “high” when the voltage tobe impressed to the one input end is smaller than the voltage to beimpressed to the other input end.

Stated further specifically, the detection circuit comprises aphotocoupler which is connected to an output end of the first comparatorand to an output end of the second comparator. The photocouplercomprises a light-emitting diode for emitting light corresponding topotentials of the output ends, and a phototransistor to be turned on bylight-emitting of the light-emitting diode, and detects leakageoccurrence based on on/off of the phototransistor.

Stated furthermore specifically, values of resistance for the first andthe second voltage dividing resistors interposed on the first currentline, for the first and the second protection resistors interposed onthe second current line, and for the first and the second detectionresistors interposed on the second current line are so adjusted that inthe event of the leakage occurrence at any point of connection betweenthe plurality of cells constituting the cell unit, the dead zone indetecting leakage, wherein a voltage to be impressed to the one inputend of the first comparator is greater than a reference voltage to beimpressed to the other input end, and a voltage to be impressed to oneinput end of the second comparator is smaller than a reference voltageto be impressed to the other input end, is contained in an inside of apotential distribution region corresponding to one cell, which isincluded in potential distribution generated between opposite electrodesof the cell unit.

Consequently, even in the event of the leakage occurrence at any pointof connection between the plurality of cells comprising the cell unit,the potential at the point of the leakage occurrence does not correspondto the dead zone.

The leakage detection circuit for use in the power source deviceembodying the invention, as described above, the leakage occurrence atthe point of connection between a plurality of cells comprising the cellunit can be reliably detected. This can forestall electric shockaccidents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example construction of a leakage detection circuitembodying the invention;

FIG. 2 is a diagram for indicating a point having a possibility ofleakage occurrence in a cell unit;

FIG. 3 is a graph showing a relationship between a potential of leakageoccurrence and an input voltage to two Op-Amps;

FIG. 4 is a graph showing an example for eliminating the problem of adead zone by altering a circuit constant as in the same manner as FIG.3;

FIG. 5 is a diagram showing an equivalent circuit which is part of acircuit shown in FIG. 1 and a circuit constant; and

FIG. 6 is a circuit diagram showing the construction of a conventionalleakage detection circuit.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to the drawings, a detailed description will be given ofa leakage detection circuit embodying the invention for use in a powersource unit, which is mounted on an electric motor vehicle.

As shown in FIG. 1, two cell modules 12A, 12B comprises a plurality ofsecondary cells 12 a, which are connected in series. The two cellmodules 12A, 12B constitute a cell unit 12 which is mounted on a vehiclebody through an insulation member. Nickel hydrogen cells, etc. are usedas secondary cells 12 a. Obtained between a positive terminal and anegative terminal of the cell unit 12 is, for example, 300V, in totalvoltage.

A positive-side power line 10 a and a negative-side power line 10 bextend, respectively, from a positive and a negative terminals of thecell unit 12, and are connected to an inverter which is not shown. Theinverter comprises a switching element such as IGBT (Insulated GateBipolar Transistor), etc. and converts d.c. power to a.c. power tosupply the power to a drive motor.

The leakage detection circuit 10 of the invention comprises a firstcurrent line 34 and a second current line 22 which are connected to eachother in parallel between the positive-side power line 10 a and thenegative-side power line 10 b. Interposed on the first current line 34are a first voltage dividing resistor 30 and a second voltage dividingresistor 32 each having a value of resistance of 56 kΩ, which arerelated each other in parallel. Interposed on the second current line 22are a first protection resistor 14 and a second protection resistor 16each having a high value of resistance of 1MΩ, which are related eachother in parallel. Interposed between the two protection resistors 14,16 are a first detection resistor 18 and a second detection resistor 20each having a value of resistance of 22 kΩ, which are related each otherin parallel.

A point of connection 24 between the first and the second detectionresistors 18, 20 which are interposed on the second current line 22 isconnected to a ground (vehicle body) through an insulation resistor 28having a high value of resistance of 6MΩ.

The leakage detection circuit of the invention comprises a first Op-Amp36 and a second Op-Amp 38. A point of connection 35 (reference point)between the first voltage dividing resistor 30 and the second voltagedividing resistor 32 which is interposed on the first current line 34 isconnected to a negative input terminal of the first Op-Amp 36 through acurrent limiting resistor 44 having a value of resistance of 100 kΩ, andis connected to a positive terminal of the second Op-Amp 38 through acurrent limiting resistor 46 having a value of resistance of 100 kΩ. Apoint of connection P1 between the first protection resistor 14 and thefirst detection resistor 18 which are interposed on the second currentline 22 is connected to a positive input terminal of the first Op-Amp 36through a current limiting resistor 42 having a value of resistance of100 kΩ. A point of connection P2 between the second protection resistor16 and the second detection resistor 20 is connected to a negative inputterminal of the second Op-Amp 38 through a current limiting resistor 48having a value of resistance of 100 kΩ.

Op-Amps 36, 38 are given defined power source voltages, +15V, −15V,respectively, as illustrated.

The leakage detection circuit of the present invention comprises aphotocoupler 40 having a light-emitting diode 50 and a phototransistor52. An output end of the first Op-Amp 36 and that of the second Op-Amp38 are interconnected to, respectively, via resistors 54, 56, and apoint of the interconnection is connected to the light-emitting diode50. The leakage occurrence causes the light-emitting diode to emitlight, as will be described below, to have the phototransistor 52electrically conducted, notifying the leakage occurrence to amicrocomputer not shown.

When the leakage does not occur, the cell unit 12 of high voltage isinsulated from the grounding (vehicle body) 26 by an insulation resistor28 to be in a floating state, so that leakage current does not flowthrough the first and the second detection resistors, 18, 20 of thesecond current line 22. Accordingly, the leakage voltage will not begenerated between opposite ends of any of the detection resistors 18,20.

For example, suppose a negative terminal of the cell unit 12 is groundedby fault via a ground resistor 58 having a resistance value of 100 kΩ,as shown in FIG. 1, causing leakage occurrence. In this case, thenegative-side power line 10 b extending from a negative terminal of thecell unit 12 is grounded to the grounding 26(vehicle) via the groundresistor 58, as shown in FIG. 1. Accordingly, the leakage current flowsthrough the first and second protection resistors 14, 16, the firstdetection and second detection resistors 18, 20, the insulation resistor28, and the ground resistor 58, via the grounding 26, generating avoltage V1 and a voltage V2 resulted from the leakage between oppositeends of each of the first and second detection resistors 18, 20.

Voltage differences V1IN and V2IN between each of the voltages V1, V2and a reference voltage Vc impressed from the reference point 35 of thefirst current line 34 are respectively input to the first and secondOp-Amps 36, 38. The voltage differences are compared with thepredetermined values, respectively, in the Op-Amps 36, 38. When theinput voltages V1IN and V2IN become greater than the predeterminedvalue, the Op-Amps 36, 38 each produce output voltages V1OUT and V2OUT.

In the example shown in FIG. 1, the negative terminal of the cell unit12 is grounded by fault via the ground resistor 58 having a resistancevalue of 100 kΩ, and a leakage current ig flows, forming an equivalentcircuit shown in FIG. 5. With the equivalent circuit, a followingrelationship is obtained, wherein i is a circuit current.

i=138.5V/1.022MΩ=135.5 μA

ig=138.5V/6.1MΩ=22.7 μA

V 1=(135.5 μA+22.7 μA)×22 kΩ=3.48V

V 2=135.5 μA×22 kΩ=2.98V

V 1 IN=(138.5V+3.48V)−150V=−8.02V

V 2 IN=(138.5V−2.98V)−150V=−14.48V

Accordingly, V1OUT=−15V and V2OUT=+15V, with the result that thelight-emitting diode 50 of the photocoupler 40 emits light to have thephototransistor 52 turned on. The microcomputer detects that a signalfrom the phototransistor 52 is changed over from high to low, therebydetermining the leakage occurrence.

Furthermore, in the case where the leakage occurs at a positive terminalside of the cell unit 12, the same result as described is obtained.

When the leakage does not occur, only the circuit current i isgenerated, V1IN=3.23V, V2IN=−3.23V, V1OUT=+15V, and V2OUT=+15V, to havethe photocoupler 40 held off.

With the cell unit 12, power lines extend from the positive and negativeterminals of the cell unit 12, respectively, as shown in FIG. 2, andvoltage detection lines extend from points of connection between cells12 a, and lines further extend from points of connection between thecell modules 12A and 12B to a safety switch, so that if any line of thelines described above is grounded by fault, the leakage occurs. There isa possibility of the leakage occurrence at each point indicated by crossmarks shown in FIG. 2.

Input voltages V1IN and V2IN shown in FIG. 1 are found as for each pointwherein there is a possibility of the leakage occurrence, and the resultfound is given as follows. In this case, the cell unit 12 comprises 16cells, and the unit has an output voltage of 240V(=15V×16).

(1) power line (±)/d.c. side of inverter (±) ±120 V (2) voltagedetection line of cell module ±15 V × 8 points (3) safety switch line   0 V

FIG. 3 is a graph showing input voltage V1IN and V2IN, respectively, ina solid line and in a broken line when the leakage occurs at each point,wherein a potential at each point of leakage occurrence is plotted asthe X-axis and a potential of input voltage V1IN and V2IN is plotted asthe Y-axis in the case where the ground resistor 58 is 100 kΩ.

FIG. 3 shows that the following three cases are present depending on apoint of leakage occurrence: {circle around (1)} V1IN>0, V2IN<0, {circlearound (2)} V1IN<0, V2IN<0, {circle around (3)} V1IN>0. In the cases of{circle around (2)} and {circle around (3)} the photocoupler is turnedon to permit the leakage detection, while in the case of {circle around(1)} the photocoupler is not turned on, and thereby the leakage cannotbe detected. That is, with the leakage detection circuit 10 having thecircuit constant described above, the leakage cannot be detected atpoints of leakage within ±45V shown in FIG. 3, whereby generating a deadzone.

In this embodiment the influence of the dead zone is avoided byadjusting the circuit constant of the leakage detection circuit 10, aswill be described below.

Table 1 shows the result of calculating the input voltage V1IN and V2INat representative points (±120V, ±90V, ±30V, 0V) out of the points (1),(2), and (3) each having a possibility of the leakage occurrence asdescribed above.

TABLE 1 leak. Resist. −120V −90V −30V 0V 30V 90V 120V V1IN short −6.63−4.33 0.28 2.58 4.89 9.49 11.8 circuit V2IN −11.8 −9.49 −4.89 −2.58−0.28 4.33 6.63 V1IN 100k −6.49 −4.22 0.31 2.58 4.85 9.39 11.66 V2IN−11.66 −9.39 −4.85 −2.58 −0.31 4.22 6.49

In order to permit the leakage detection at any point wherein there is apossibility of the leakage occurrence, both of the input voltage V1Inand V2In at the point of the leakage occurrence should be made positiveor negative. The conditions for this are as follows:

(1) X-intercept of the input voltage V1IN and V2IN shown in FIG. 3 is inthe range of 0 to 15V or 0 to −15V.

(2) the intersection of a solid line showing variation of the leakagedetection voltage Va (potential of P1 in FIG. 1), Vb (potential of P2 inFIG. 1) and the reference potential Vc is in the range of 0 to 15V or 0to −15V.

FIG. 2 shows the result obtained by altering the circuit constant so asto fulfill the above conditions.

TABLE 2 R1(k) R2(k) R3(k) R4(k) RC1(k) RC2(k) ZDC1 ZDC2 Be- 1000 22 221000 56 56 15V 15V fore alter. After 3450 10 10 3300 58.5 56 15V 15Valter.

Furthermore, FIG. 4 shows a graph in the same manner as FIG. 3 in thecase where the ground resistor 58 is 100 kΩ with the leakage detectioncircuit 10 after the alteration of the circuit constant.

Table 3 further shows the result obtained by calculating the inputvoltage V1In and V2IN after the alteration of the circuit constant ateach point of leakage occurrence.

TABLE 3 leak. Resist. −120V −90V −30V 0V 30V 90V 120V V1IN short −25.42−18.84 −5.68 0.9 7.48 20.64 27.21 (Va) circuit (−28.04) (−21.46) (−8.3)(−1.72) (4.86) (18.02) (24.59) V2IN −26.12 −19.54 −6.39 0.19 6.77 19.9226.5 (Vb) (−28.74) (−22.16) (−9.01) (−2.43) (4.15) (17.3) (23.88) V1IN100k −25.09 −18.59 −5.6 0.89 7.39 20.37 26.87 (Va) (−27.71) (−21.21)(−8.22) (−1.73) (4.77) (17.75) (24.25) V2IN −25.79 −19.3 −6.31 0.18 6.6819.66 26.16 (Vb) (−28.41) (21.92) (−8.93) (−2.44) (4.06) (17.04) (23.54)

According to the above calculation results, it is found that the leakagecan be detected as for any point wherein there is a possibility ofleakage occurrence by altering the circuit constant, i.e. by suitablyadjusting the ratio of the protection resistor to the detection resistor(value of the leakage detection voltage Va and that of Vb) and the ratioof the voltage dividing resistor (value of the reference voltage Vc).

With the leakage detection circuit 10 shown in FIG. 1, the point whereinthere is a possibility of the leakage occurrence can be identified inadvance, so that the leakage can be detected at each point by settingeach value of the protection, detection, and voltage dividing resistorsso as to shift the dead zone of the leakage detection from the leakagepoint.

What is claimed is:
 1. A leakage detection circuit for use in a powersource device provided with a cell unit comprising a plurality of cells,the leakage detection circuit for use in the power source device beingcharacterized in that the circuit comprises: a first current path beingconnected to opposite electrodes of the cell unit, and having areference point generating a reference voltage corresponding topotential difference between the opposite electrodes, a second currentpath being connected to the opposite electrodes of the cell unit, andhaving three points which are different in potential difference, thethree points of which an intermediate point is connected to a groundingvia an insulation resistor, a first and second comparators having oneinput end to which voltage is applied from each of the two pointsdivided by the intermediate point of the second current path, and havingthe other input end to which reference voltage is applied from thereference point of the first current path, and a detection circuitdetecting leakage occurrence based on outputs of the first and thesecond comparators.
 2. A leakage detection circuit for use in a powersource device according to claim 1 wherein a circuit constant of thefirst and the second current paths is so adjusted that in the event ofleakage occurrence at any point of connection between the cellsconstituting the cell unit, a dead zone in detecting leakage based onthe outputs given by the first and the second comparators is containedin an inside of potential distribution region corresponding to one cell,which is included in potential distribution generated between oppositeelectrodes of the cell unit.
 3. A leakage detection circuit for use in apower source unit provided with a cell unit comprising a plurality ofcells, the leakage detection circuit for use in the power source devicebeing characterized in that the circuit comprises: a first current linehaving opposite ends connected to opposite electrodes, respectively, ofthe cell unit, and having first and second voltage dividing resistorsconnected in series each other, and having the resistors interposedbetween the opposite ends, a second current line having opposite endsconnected to opposite electrodes, respectively, of the cell unit, andhaving connected in series sequentially a first protection resistor, afirst detection resistor, a second detection resistor, and a secondprotection resistor, and having the resistors interposed between theopposite ends, a grounding connection line connecting to a grounding viaan insulation resistor a point of connection between the first detectionresistor and the second detection resistor which are interposed on thesecond current line, a first comparator having one input end connectedto a point of connection between the first protection resistor and thefirst detection resistor which are interposed on the second currentline, and having the other input end connected to a point of connectionbetween the first voltage dividing resistor and the second voltagedividing resistor which are interposed on the first current line, asecond comparator having one input end connected to a point ofconnection between the second detection resistor and the secondprotection resistor which are interposed on the second current line, andhaving the other input end connected to a point of connection betweenthe first voltage dividing resistor and the second voltage dividingresistor which are interposed on the first current line, and a detectioncircuit detecting leakage occurrence based on outputs of the first andthe second comparators.
 4. A leakage detection circuit for use in apower source device according to claim 3 wherein the first and thesecond comparators each outputs two signals different in potentialcorresponding to magnitude relation between a voltage impressed to oneinput end and a reference voltage impressed to the other input end.
 5. Aleakage detection circuit for use in a power source device according toclaim 3 wherein the circuit comprises a photocoupler which is connectedto an output end of the first comparator and to an output end of thesecond comparator, and which comprises a light-emitting diode foremitting light corresponding to potentials of the output ends and aphototransistor to be turned on by light-emitting of the light-emittingdiode, and the circuit detects leakage occurrence based on on/off of thephototransistor.
 6. A leakage detection circuit for use in a powersource device according to claim 3 wherein a dead zone in detectingleakage is generated when a voltage to be impressed to one input end ofthe first comparator is greater than a reference voltage to be impressedto the other input end, and when a voltage to be impressed to one inputend of the second comparator is smaller than a reference voltage to beimpressed to the other input end.
 7. A leakage detection circuit for usein a power source device according to claim 3 wherein in the event ofthe leakage occurrence at any point of connection between the pluralityof cells constituting the cell unit, the dead zone in detecting leakagebased on the outputs of the first and the second comparators iscontained in an inside of a potential distribution region correspondingto one cell, which is included in potential distribution generatedbetween the opposite electrodes of the cell unit.
 8. A leakage detectioncircuit for use in a power source device according to claim 7 whereinvalues of resistance for the first and the second voltage dividingresistors which are interposed on the first current line, for the firstand the second protection resistors, and for the first and the seconddetection resistors which are interposed on the second current line areso adjusted as to serve as a circuit constant of the first and thesecond current line.